Equilibrium Calculations

Introduction

• Types of Equilibrium Calculations:
  • Calculation of an equilibrium constant
  • Calculation of missing equilibrium concentration or partial pressure
  • Calculation of equilibrium concentrations (or partial pressures) from initial concentrations (or partial pressures)

Manipulating Equilibrium Constants

• The equilibrium constant of a reaction in the reverse reaction is the reciprocal of the equilibrium constant of the forward reaction
• The equilibrium constant of a reaction that has been multiplied by a number is the equilibrium constant raised to a power that is equal to that number
• The equilibrium constant for a net reaction made up of two or more steps is the product of the equilibrium constants for the individual steps.

Solving Equilibrium Problems

• All equilibrium problems require the correct expression for K  (or Q).
• They can be divided into 4 types.  Two are very easy, the third more complicated, the fourth more complicated, but unfortunately, more common.
  • All concentrations (or pressures ) are given, find K.
  • Simply substitute the given values into the equilibrium expression.
  • K is given.  All but one of the equilibrium concentrations are given, find the other one.
  •  Finding K, when all the initial concentrations are known, and ONE equilibrium concentration is given.
  • It is necessary to set up a reaction table, sometimes called an “ICE chart” to find ALL the equilibrium concentrations.   
  • THEN, you can put those values into the equilibrium equation to find K. 
  • K is known, initial conc. are known, find one or more FINAL concentration.

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